The present invention relates to a rapid exhausting mechanism in a pump unit which is suitable for a small-sized sphygmomanometer for measuring blood pressure at a wrist, for example.
Conventionally, a small-sized sphygmomanometer is composed so that, for example, a cuff wound around an upper arm is pressurized to a predetermined pressure level by a small-sized air pump, the pressure in the cuff is gradually lowered at a constant-speed by a normal exhausting mechanism after the blood flow is interrupted once by pressing the artery, patterns of the pressure inside the cuff and vibration amplitude incidental to pulsation of the artery are processed by a microcomputer, and the systolic blood pressure and diastolic blood pressure are measured. The rapid exhausting mechanism is to instantaneously exhaust air in the cuff after the measuring process is over, and it is necessary that no air leaks when carrying out pressurization and measurement.
Generally, it is preferable that characteristics of the normal exhausting mechanism used for a sphygmomanometer reside in a linear decrease in the pressure inside the cuff at a constant speed of 3 mmHg through 4 mmHg per second or so as time elapses and characteristics of the rapid exhausting mechanism reside in a quick descent of the pressure as time elapses.
FIG. 3 shows such a pump unit equipped with respective exhausting mechanism as described above. In the same drawing, the pump unit 1 is composed of a pump section 2 driven by an electric motor, a normal exhausting mechanism 3 for exhausting air at a constant speed through, for example, a slit, a rapid exhausting mechanism 4 driven by a plunger, and a tubular body 5 having flexibility.
The normal exhausting mechanism 3 and rapid exhausting mechanism 4 are provided separately from the pump section 2, and these components are connected by the tubular body 5. The tubular body 5 connects an exhaust port 6 of the pump section 2, the normal exhausting mechanism 3 and rapid exhausting mechanism 4 with each other. In addition, the same tubular body 5 is connected to a cuff (not illustrated) wound around, for example, an upper arm. An air path 8 which communicates with a pump chamber 7 of the pump section 2, normal exhausting mechanism 3, rapid exhausting mechanism 4 and the cuff is formed inside the tubular body 5.
In the pump unit 1 thus constructed, as the pump section 2 is driven, and air is taken from the outside into the pump chamber 7, the air in the pump chamber 7 is sent into a cuff through the air path 8. When the pressure in the cuff is pressurized to a predetermined pressure level, air exhaust in the air path 8 is commenced by the normal exhausting mechanism 3. In synchronization therewith, air of a greater volume than the volume of air exhausted from the normal exhausting mechanism 3 is sent into the cuff from the pump chamber 7.
Also, as the cuff is internally pressurized to a predetermined pressure level, the pump section 2 stops its operation, whereby the pressure inside the cuff is gradually lowered by utilizing normal exhaust of the normal exhausting mechanism 3. At this time, patterns of the pressure inside the cuff and vibration amplitudes incidental to pulsation of the artery are processed by a microcomputer, and the systolic blood pressure and diastolic blood pressure are measured. After the measurement is processed, the air in the cuff is discharged with a breath by the rapid exhausting mechanism 4.
However, in the pump unit 1, the normal exhausting mechanism 3 and rapid exhausting mechanism 4 are provided separately from the pump section 2. Therefore, the pump unit 1 has a number of components, and its structure is also complicated. In addition, since the rapid exhausting mechanism 4 of the pump unit 1 employs an exclusive plunger as an actuator, the mechanism 4 becomes heavy and large-sized, resulting in an increase in production costs.
Japanese Patent Publication No. 2000-352379A proposes a relatively small-sized exhausting mechanism. This configuration includes, as an exhausting mechanism in a diaphragm type pump equipped with an actuator for vertically moving a diaphragm, an intake one-way valve having a valve body which is made of a flexible member and is provided so as to correspond to an intake port, and an exhaust one-way valve having a valve body which is made of a flexible member and is provided so as to correspond to an exhaust port. Here, minute concave and convex irregularities are provided on the surface to which the valve bodies comes in contact with, thereby preventing the valve bodies are adhered thereon. The respective one-way valves can be opened in minute differences in pressure between the upstream side and downstream side.
However, it is ignored air leakage at the position where the minute concave and convex irregularities are provided, which is caused when the upstream side is at a high pressure level.